WO2013079588A1

WO2013079588A1 - Method for regenerating aqueous dispersions and cell package for electrodialysis

Info

Publication number: WO2013079588A1
Application number: PCT/EP2012/073950
Authority: WO
Inventors: Klaus Lepa; Ulrich Dawidowski
Original assignee: Henkel Ag & Co. Kgaa
Priority date: 2011-11-29
Filing date: 2012-11-29
Publication date: 2013-06-06
Also published as: US9511325B2; DE102011087314A1; EP2785438A1; EP2785438B1; CN104066496A; KR20140106530A; IN2014CN03938A; US20140251810A1; CN104066496B

Abstract

The present invention relates to a method for reducing the ionic strength or certain polyvalent ions in aqueous dispersions of organic binding agents or inorganic solid bodies by means of electrodialysis and a cell package (100), which is suitable for the method according to the invention. The method according to the invention permits aqueous compositions of the dispersed components to be stabilised by regulating the ionic strength or the concentration of certain polyvalent ions and hence significantly increase the durability and throughput times of coating baths for example. More particularly, the process is used in the removal of polyvalent metal cations from anionically stabilised aqueous binding agent dispersions. A special application exists in removing from autophoretic baths, which contain anionically dispersed organic binding agents and possibly inorganic pigments for forming protective layers on metallic components, polyvalent cations of zinc, iron and aluminium, which accumulate in the bath due to pickling processes when a number of components, the surfaces of which are produced at least partially from zinc, iron and/or aluminium, are passed through.

Description

"Process for the regeneration of aqueous dispersions

as well as cell pack for electrodialysis "

The present invention relates to a method for reducing the ionic strength or certain polyvalent ions in aqueous dispersions of organic binders or inorganic solids using electrodialysis and a cell packet which is suitable for the inventive method. The process according to the invention makes it possible to stabilize aqueous compositions of the dispersed components by regulating the ionic strength or the concentration of specific polyvalent ions and thus significantly increasing stating and processing times, for example of coating baths. In particular, the process finds utility in the removal of polyvalent metal cations from anionically stabilized aqueous binder dispersions. A special application is to remove polyvalent cations of zinc, iron and aluminum from the autodrainable baths containing anionically dispersed organic binders and optionally inorganic pigments for the formation of protective coatings on metal components Components whose surfaces are at least partially made of zinc, iron and / or aluminum, due to

Enrich pickling processes.

Aqueous compositions containing dispersed active components are used in a variety of industrial processes for surface treatment of components and semi-finished products, wherein the components and semi-finished products are usually brought into contact with the aqueous dispersion by spraying or dipping. The aqueous dispersions, which are brought into contact with the components and semifinished products for the purpose of tempering the surfaces, can generally be applied in many cases before the dispersion of active components is depleted to such an extent that a metered addition of active components for the desired

Treatment success must be made. The aqueous dispersions used for the surface treatment are thus collected after bringing into contact with the component or stored in immersion baths and optionally treated and regenerated to again for

Surface treatment can be applied. Such a recurrent or continuous application results in impurities adhering to the components being taken up by the aqueous dispersions and concentrated over time. Particularly critical is the salting of the aqueous dispersions, ie the introduction of salts, as this significantly reduces the stability of the dispersed active components. As the ionic strength increases, dispersions tend to coagulate as the

electrostatic repulsive forces between similar charged electrolytic

Double layers of the dispersed active components are significantly attenuated, so that the thermodynamically favored coagulation is less inhibited. Technical

Problems arise the progressive coagulation of the dispersed active components on the one hand, because sedimented active components are no longer available for the surface treatment, and on the other hand, in that the result of the surface treatment often depends on the size distribution of the dispersed active components.

Thus, the activation of automobile bodies succeeds in protecting against corrosion

Phosphating with aqueous colloidal compositions of sparingly soluble

Phosphates or titanium salts, which form on the metal surfaces crystallization nuclei for the subsequent phosphating. Such activation baths are described in EP 0977908 or in WO 94/029495. The ability to form

Crystallization nuclei have the active components only if they do not exceed a certain particle size. The bodies are usually brought into contact with the activating solution by spraying or dipping in the phosphating line of automobile production, whereby contaminants, in particular salts, are introduced from the body into the activating solution. The entrainment of certain interfering polyvalent ions, for example, from the metal body to be treated, in such phosphating activation baths can lead to faster consumption of the activation solution due to the associated accelerated coagulation, which is therefore either discard early or be regenerated via the addition of concentrates got to. Such specific salination or entrainment of interfering ions is therefore tolerable only in a certain concentration range.

In particular, the stability of organic binder dispersions is influenced by the entry of polyvalent ions. For example, aluminum salts are often used as an aid for the separation of paint components in the wet scrubbing of paint booths in the automotive industry. However, in many applications maintaining the stability of aqueous binder dispersions is paramount. So be

Automotive bodies after the corrosion-protective phosphating usually provided with a dip. The dip paint is a water-based dispersion of one or more organic binders whose deposition on the body when immersed in the dip paint without power or by applying an external voltage succeed. Of the The deposition mechanism of the binder in the dipping paint is based on the fact that the surface charge of the dispersed binder in close proximity to the surface of the body is lifted, so that coagulation and deposition of

Binder particles takes place. Dipping paints therefore tend to coagulate due to the application, when the concentration of a certain type of ion is exceeded. Conversely, this means that the introduction or concentration of certain ions, the stability of the dip paint can greatly reduce. Typically, anodic or autophoretic dip coatings consist essentially of anionically stabilized binder components that can rapidly coagulate in the presence of polyvalent cations.

There is therefore a need to regulate the ionic strength or the concentration of certain polyvalent ions in aqueous dispersions of inorganic solids and / or organic binders in order to maintain the stability of the dispersions over a relatively long period of time. For this purpose, it is necessary to establish a method which brings about a selective depletion of polyvalent cations in aqueous dispersions, but without appreciably reducing the proportion of dispersed active components.

In the prior art exist for this purpose various established separation processes in which a selective mass transfer takes place through membranes. Of course, it is well known to those skilled in the art that they can use filtration with cut-off limits just below the average particle size of the dispersed active components to separate the active components from the aqueous phase. However, so-called "cake-forming" filtration methods are not suitable for obtaining a filtrate containing the excess

or interfering polyvalent ions, since the filter cake consisting of the retained active components can be redispersed only at great expense. Membrane filtration methods, which are operated as cross-flow filtration, are in principle suitable for the recovery of a filtrate, wherein the retentate can be removed using ion-exchanging membranes also selectively interfering ions. However, in so-called cross-flow filtration, the aqueous dispersion is subjected to high shear stresses, which result in coagulation of the dispersed constituents in the filter unit and in the pumps. This phenomenon often occurs in dispersions of organic binders, so that the cross-flow filtration, for example, of

Dipcoats for reducing the ionic strength can not be applied. The

Filtration methods have in common that the excess or interfering polyvalent ions must first be removed from the filtrate, for example by precipitation, before the filtrate can be recycled to the dispersion and, overall, a reduction in the ionic strength or the concentration of certain polyvalent ions in the Dispersion results. The application of filtration methods is therefore extremely costly in terms of process engineering even in cases in which a sufficiently high stability of the dispersion against shear stress is given for the reduction of the ionic strength.

DE 3431276 discloses a process for reducing the ionic strength in resin dispersions, which is suitable for electroless self-deposition of organic coatings on metallic surfaces, preferably iron surfaces. The reduction in ionic strength, especially the concentration of iron ions, is also performed here to stabilize the binder system in the autodepositing bath against coagulation.

DE 3431276 avoids the problem that high shear stresses lead to coagulation of the paint components, in that the filtrate, ie the aqueous phase which is to be enriched with the interfering ions, is circulated, while the dispersion itself does not flow against ion-exchanging membranes of the filter module and only in contact with them. With this method, a controlled reduction of the ionic load in the aqueous dispersion of the binder is possible, but the filter module must be regularly backwashed to remove binder particles on the membrane surfaces, to ensure a consistent separation performance.

WO 02/18029 discloses a process for the selective separation of polyvalent cations from an autodepositing bath containing an organic binder dispersed in water that tends to coagulate rapidly in the presence of polyvalent cations of the elements iron and zinc. According to this method, an acidic selective cation exchanger is charged with the bath enriched with polyvalent cations, thus achieving a reduction of the ions. The cation exchanger must be regenerated at regular intervals.

The object of the present invention is an alternative method for

Reduction of ionic strength or the concentration of polyvalent ions in an aqueous dispersion of organic binder and / or inorganic solid, in which the concentration of certain polyvalent cations or anions in the aqueous dispersion can be effectively reduced, without effectively removing dispersed active components irrevocably. The process should be suitable for use in the continuous operation of a surface treatment process, the

Reduction of the ionic strength or the concentration of certain polyvalent ions should be carried out with the least possible maintenance. The procedure should

be particularly suitable for in acidic aqueous Abscheidebädern containing dispersed organic binders, which are autophoretically adjusted, the concentration of the Coagulation of the binder to effectively regulate potentially causing polyvalent ions, especially iron ions, zinc ions and aluminum ions.

This object is achieved by an electrodialysis method,

in which a volume flow V _{B of} a bath liquid containing a dispersed organic binder and / or a dispersed inorganic solid and polyvalent cations and / or polyvalent anions from an aqueous bath containing the bath liquid and a volume flow V _{K of} an aqueous concentrate from a concentrate reservoir vorratend the concentrate in a cell pack for electrodialysis comprising a membrane stack of a plurality of spaced-apart ones

Membranes which, in the event that troublesome polyvalent cations are contained in the bath liquid, exclusively cation exchangers, and in the event that troublesome polyvalent anions are contained in the bath liquid exclusively

Anionenaustauscher includes, and electrically conductive current collector, the

Limit membrane stacks on both sides in stacking direction, feed in,

in which the volume flows V _B and V _K within the cell packet into partial volume flows δ, (ν _Β ) and δ, (ν _κ ) decay, the spatially separated from each other orthogonal to

Surface normals of a series of membranes of the membrane stack to flow through the segments formed by immediately adjacent and spaced apart membranes of this series, with segments of the series of membranes through which only a partial volume flow δ, (ν _Β ) flows through the bath liquid, with such segments of the series of membranes, through which only a partial volume flow δ, (ν _κ ) of the concentrate flows, alternating in the stacking direction, wherein the

Bath liquid within the segments of the series of membranes adjacent

Membranes flow laminarly,

wherein each of the outer membranes of the membrane stack on the side facing the immediately adjacent pantograph is either in contact with an aqueous electrolyte spatially separated by the segment formed by the respective current collector and the respective outer membrane from the aqueous concentrate and the bath liquid with a partial volume flow δ, (ν _κ ) of the aqueous concentrate is flown,

in which an electric voltage is temporarily or permanently applied to the electrically conductive current collectors, which are in contact with the aqueous electrolyte and / or the aqueous concentrate, wherein the electrical voltage is sufficiently high to prevent the electrolytic decomposition of the aqueous electrolyte and / or the Concentrate, and in which the partial volume flows δ, (ν _Β ) of the bath liquid are combined after passing through the membrane stack and fed back into the aqueous bath, while the partial volume flows δ _ί (ν _κ ) of the aqueous concentrate after passing through the

Membrane stack combined and transferred at least partially into the concentrate reservoir.

For the purposes of the present invention, such polyvalent ions are disturbing, which in the

Bad liquid when exceeding a threshold concentration reduce the quality of the bath based on the particular application. Accordingly, interfering polyvalent ions are always coagulating ions in bath liquids containing organic binders and / or inorganic solids.

As cation exchangers or anion exchangers according to the invention apply polymers

Materials with ionogenic functional groups and free - moving counterions, in which the ratio of cations to anions or anions to cations in the

Ion exchanger in each case based on the freely movable counterions is greater than 1.

The inventive method allows due to the exclusive use of selectively ion-exchanging membranes of the same type, which are respectively flowed around on one side of the bath liquid and on the other side of the aqueous concentrate, that migration of the interfering polyvalent cations or anions from the bath liquid into the aqueous Concentrate takes place, whereby an enrichment of the interfering polyvalent ions is achieved in the concentrate. Likewise an enrichment of interfering polyvalent cations is achieved directly in that aqueous electrolyte which is in contact with the current collector connected as a cathode, while interfering polyvalent anions are directly enriched in the electrolyte which is connected to the anode connected

Pantograph is in contact. At the same time, the exclusive use of selectively ion-exchanging membranes of the same type avoids that the dispersed constituents mostly due to their for charging the interfering polyvalent ions

coagulate opposite surface charge at the membrane surfaces.

At the same time, in the method according to the invention, due to the laminar flow of the ion exchange membranes with the bath liquid, there is a very moderate shear stress within the cell stack. Coagulation of the dispersed solid components induced by shear stress of the bath liquid is likewise avoided in this way, so that neither coagulum enters the bath nor blocks the cell packet in the segments in which the bath liquid flows. The laminar flow of the membranes from the bath liquid is inventively characterized in that the bath liquid outside a laminar boundary layer follows the course of the membrane and the flow is not torn or swirled.

For this purpose, at least one of the following two conditions is fulfilled in a preferred process according to the invention:

i) The dimensionless Reynolds number defined as the product of mean flow velocity in the segments of the membrane stack through which the bath flows

Spacing the membranes within the same segments through which

Partial volume flow δ, (ν _Β ) flows, divided by the kinematic viscosity of the bath liquid is less than 2000, more preferably less than 1000, in particular less than 100. The Reynolds number is calculated as follows: υ

Re: Reynolds number

v: mean flow rate in the flowed through by the bath liquid

Segments of the Membrane Stack [m / s]

d: spacing of the membranes in the direction of their surface normals within the

Segments through which the bath fluid flows [m]

v: kinematic viscosity of the bath liquid at the respective temperature of the bath

Bath liquid [mV ¹ ] ii) The ratio of mean flow velocity of the bath liquid in meters per second within the segments of the cell stack through which the bath liquid flows with the partial volume flows δ, (ν _Β ) for spacing the membranes in their direction

Area normal within these segments in meters is less than 100, preferably less than 20.

The average flow velocity is preferably to be calculated theoretically from the respective partial volume flow δ, (ν _Β ), the maximum width of the interior of the respective segment bounded by the membrane spacer orthogonal to the flow direction and a volume factor as follows:

y_ (V _B )

d -l-x (Vss)

V: mean flow velocity of the bath liquid [m / s]

8i (V _B ): partial volume flow of the bath fluid within the segment [m ³ / s]

d: spacing of the membranes of the segment in the direction of their Surface normals [m]

I: maximum width of the interior of the membrane spacer limited by the

respective segment orthogonal to the flow direction and orthogonal to

Surface normals of the membranes separated from the segment [m]

x (V _B ): Segment volume factor, which is the proportion of free fluid-permeable volume

within the segment flowed through by the respective partial volume flow δ, (ν _Β ) indicates [0 <x (V _B ) <1]

The segments of the cell stack are the space volumes bounded by immediately adjacent membranes and the membrane spacers ("segment volumes") within which the partial volume flows δ, (ν _Β ) or δ _ί (ν _κ ) flow separately from one another.

The bath liquid in the process according to the invention at 20 ° C. preferably has a dynamic viscosity at the respective temperature of the bath liquid of at least

0.8 mPas and not more than 20 mPas, while the flow of the bath liquid orthogonal to the surface normal of the membranes of the cell packet with an average flow rate of preferably not more than 0.1 m / s, more preferably not more than 0.01 m / s takes place.

In a preferred method, the following condition also exists within the segments of the cell packet formed by the series of membranes: d ² -x (V _B ) -8 i (V _K )

is greater than 3, preferably greater than 4, wherein

δί (ν _Β ): the partial volume flow of the bath liquid within the segment [m3 / s], δί (ν _Β ): the partial volume flow of the concentrate within the segment [m3 / s],

d _B , d _K : the spacing of the membranes of the respective segment in the direction of their

Surface normals [m] and

x (V _K ; V _B ): the segment volume factor that is the fraction of free fluid permeable

Indicates volume within the respective perfused segment

[0 <x (V _K ; V _B ) <1].

If this condition is additionally met, the result is a much stronger flow in the segments of the membrane stack through which the concentrate flows in comparison to the laminar flow in the segments through which the bath liquid flows. Due to the thus increased convection in the flowed through by the concentrate segments a rapid mixing of the segment volume is achieved and increases the mass transfer in the stacking direction of the membranes. In a preferred method according to the invention, the voltage applied to the

Pantograph of the cell packet is applied that a current density of at least

0, 1 mAcm ^"2 , preferably at least 1 mAcm ^{" 2} , but preferably not more than 10 mAcm ^"2 results.

Furthermore, it is preferred that a rectified electrical voltage to the

Current collector is applied and no reversal occurs during the process, the impressing of the electrical voltage is particularly preferably pulse potentiostatic, wherein the pulse duration, ie the duration of a single pulse, preferably in the range of 0.5 to 50 seconds, more preferably in the range of 0 , 8 to 2 seconds, and the pulse resting phase, ie the phase between two pulses during which no voltage is applied to the current collector, preferably in the range of 0.2 to 10 seconds, particularly preferably in the range of 0.4 to 1 second. The temporary imprint of a rectified

Tension provides the advantage that the solid components dispersed in the bath liquid, which, due to their migration in the electric field, are attracted by the bath liquid

Membranes are accumulated, can be removed in the flow field when the electrical voltage is removed, so that a possible coagulation of the dispersed solids and an associated blocking of the membrane is prevented.

In a preferred method according to the invention, the current collectors have a planar design and are in contact with the electrolyte exclusively on their inner surfaces which face the membrane stack; the current collectors are particularly preferably configured to be dimensioned to the membranes of the stack of the cell packet.

The membranes are preferably formed in the method according to the invention as rectangular areas, wherein the sides of the rectangular areas are preferably at least 0.05 m long, but preferably not longer than 1, 0 m.

The current collector can be manufactured with other corrosion resistant alloys such as nickel-molybdenum alloys (Hastelloy ^®), or pose platinum or graphite laminated metallic or metallically conductive support materials. In addition to the corrosion resistance and abrasion resistance of the electrode material requires an economic Verfahrweise that the electrode materials for the corresponding electrochemical partial reaction for the decomposition of the electrolyte should have the lowest possible overvoltage and the

Current collector therefore often in the contact area with the aqueous electrolyte and / or the aqueous concentrate are coated with precious metals of the elements platinum, ruthenium and / or iridium. In a preferred embodiment of the method the aqueous electrolyte from an electrolyte reservoir, a volume flow fed V _E of the aqueous electrolyte in the cell stack before guessing, the δ within the cell packet in the partial volume flows _(ν Ε) disintegrates, the orthogonal of the surface normal of the outer membranes

Membrane stack to flow through the segments of the cell stack formed by the current collectors and the immediately adjacent outer membranes, wherein the

Partial volume flows δ, (ν _Ε ) after passing through the segments, preferably within the

Cell packs combined and preferably at least partially transferred into the electrolyte reservoir. In this preferred embodiment, therefore, a total of three separate volume flows V _B , V _K and V _E are fed independently into the cell packet and decay there in each case orthogonal to the stacking direction extending partial volume flows. This embodiment enables the electrolytic process to be optimized independently of the concentrate due to the separate volume flows of concentrate and electrolyte, so that, for example, low decomposition voltages can be realized. Furthermore, it is advantageous that the electrolyte can be replaced or regenerated independently of the concentrate.

In addition, in a method according to the invention for reducing disruptive polyvalent ions in a bath liquid, it is preferable to separately feed a volume flow V _{E of} an aqueous electrolyte into the cell packet in the anolyte and the catholyte so as to exchange the anolyte and catholyte independently of each other or to be able to regenerate. This provides the advantage that due to the separation of the material cycles of catholyte and anolyte no steady state based on the concentration of interfering polyvalent ions within the segments of the

Membrane stack is achieved because either the catholyte in inventive use of cation exchangers or the anolyte when using anion exchangers is a sink for the polyvalent cations or anions, so that the concentration of the respective interfering polyvalent cations or anions in the catholyte or anolyte increases steadily, while steadily decreasing in all other segments of the membrane stack.

In an alternative, procedurally less expensive embodiment of the method according to the invention, no aqueous electrolyte is additionally fed into the cell stack and the membrane stack consists exclusively of membranes of the series of membranes, within which each membrane is unilaterally flowed by the bath liquid laminar and segments which are of the Bath liquid to be flowed with segments, which are flowed through by the aqueous concentrate, alternate. Consequently, in this embodiment, only the volume flows V _B and V _{K are} fed into the cell packet. The process according to the invention for this preferred case consequently reduces to an electrodialysis process for reducing interfering polyvalent ions in an aqueous bath,

in which a volume flow V _{B of} the bath liquid containing a dispersed organic binder and / or a dispersed inorganic solid as well as polyvalent cations and / or polyvalent anions from the bath containing the bath liquid and a volume flow V _{K of} an aqueous concentrate from a concentrate reservoir reservratend the concentrate into Cell pack for electrodialysis comprising a

Membrane stack which, in the event that troublesome polyvalent cations are contained in the bath liquid, exclusively cation exchanger, and in the event that troublesome polyvalent anions are contained in the bath liquid exclusively

Anionenaustauscher includes, and electrically conductive current collector, the

Limit membrane stacks on both sides in stacking direction, feed in,

Surface normals of the membranes of the membrane stack to flow through the segments formed by immediately adjacent and spaced apart membranes of this series, wherein segments, through which only one

Partial flow δ, (ν _Β ) flows through the bath liquid, with such segments through which only a partial volume flow δ, (ν _κ ) of the concentrate flows through, in

Alternate stacking direction, the bath liquid within the segments

adjacent membranes flow laminarly,

in which each of the outer membranes of the membrane stack is supplied with a partial volume flow δ, (ν _κ ) of the aqueous concentrate on the side facing the immediately adjacent current collector,

in which an electrical voltage is temporarily or permanently applied to the electrically conductive current collectors which are in contact with the aqueous concentrate, the voltage being sufficiently high to cause the electrolytic decomposition of the aqueous concentrate,

and in which the partial volume flows δ, (ν _Β ) of the bath liquid are combined after passing through the membrane stack and fed back into the aqueous bath, while the partial volume flows δ, (ν _κ ) of the aqueous concentrate after passing through the

Membrane stack combined and transferred at least partially into the concentrate reservoir. In this procedure, the concentration in the flowed through by the concentrate segments of the membrane stack and the depletion in the runs of the

Bath liquid flowed through segments of the membrane stack based on one or more cation or Anionensorten until reaching a steady state. With this comparatively moderate, but all flowed through by the concentrate segments of the

Concentration affecting membrane stack has the specific advantage that in a method according to the invention for reducing polyvalent cations in a bath liquid, precipitation of sparingly soluble hydroxides in the catholyte can be largely prevented by the method.

The partial volume flows δ, (ν _Β ), δ, (ν _κ ) and δ, (ν _Ε ), which are orthogonal to the stacking direction of

Run membranes and flow through the individual spanned from the membrane stack segments of the cell stack, are rectified in a preferred embodiment of the method according to the invention, that is, they flow through the segments of the membrane stack in a common direction.

In the process according to the invention, the aqueous electrolyte and the aqueous concentrate preferably have a specific electrical conductivity of at least 1 mScm ^-1 , more preferably at least 10 mScm ^-1 .

Preferably, the concentration of a disturbing polyvalent ion type in the concentrate of a method according to the invention is below a critical concentration. The critical concentration of a disturbing polyvalent ion type in the aqueous concentrate is the

Concentration of the same interfering polyvalent ion type in the bath liquid multiplied by the ratio of the sum of the products of charge number, concentration and

Lonenbeweglichkeit all other, the interfering type of ion same charged ion types in the concentrate to the sum of the products of charge number, concentration and ion mobility of all other, the interfering ion sort same charged ion types in the bath liquid. Accordingly, the following relationship applies to the critical concentration of interfering polyvalent ions:

X ^z i ^u i ^c i ( ^K )

£ Z _{YYY CJ} (B) critical concentration of the interfering polyvalent ion species

in the concentrate [mol / l]

Concentration of the interfering polyvalent ion species

in the bath liquid [mol / l]

Products of charge number, ion mobility and concentration of a similar to the interfering type of ion like charged ion type i in the concentrate

Products of charge number, ion mobility and concentration of a type of ion equally charged to the disturbing type of ion j

in the bath liquid

zi ^■ charge number of the ion types i, j

^'U J ionic mobility of ionic species i, j [m ² s ^"1 ^{V" 1]} concentration of ionic species i, j [mol / l]

Above this critical concentration of a disturbing polyvalent ion type in the

Concentrate is a reduction of the proportion of the same ions in the bath liquid in a method according to the invention is not effective. In a preferred method according to the invention and in particular in a method in which the electrolyte is identical to the concentrate, wherein the membrane stack exclusively membranes from the series of

Containing membranes and only the volume flows V _B and V _K are fed into the cell stack, partial volumes of the concentrate are therefore continuously or discontinuously replaced by concentrate solution containing no interfering polyvalent ions and preferably an aqueous solution having an electrical conductivity of at least 1 mScm ^"1 , or interfering polyvalent ions are removed by precipitation and filtration of the concentrate to ensure that the proportion of interfering polyvalent ions in the concentrate are not above their respective critical concentration, preferably the proportion of interfering polyvalent ions Analyzing the ions in the concentrate to at least partially replace the concentrate as it approaches the critical concentration with fresh concentrate solution or to add a reagent for precipitating the interfering polyvalent ions so that the concentration the disturbing polyvalent ions in the concentrate the respective critical

Concentration does not exceed.

In the process of the invention, it is preferred that the charge transport in the concentrate takes place predominantly by hydronium ions or hydroxide ions, since these ions in aqueous Solutions have the highest ion mobility and thus the critical concentration of the interfering polyvalent ions in the concentrate assumes a comparatively high value, so that an effective reduction of the respective interfering polyvalent ion species can take place in the bath liquid.

To remove interfering polyvalent cations from a bath liquid, the concentrate preferably has a pH below 3, more preferably below 2, but preferably the pH to avoid degradation of the cation exchangers is not below 0.5. Furthermore, in a process for removing troublesome polyvalent cations from a bath liquid, a ratio of the bath liquid to aqueous concentrate pH greater than 1 is preferred, in particular, the pH of the concentrate is at least one unit lower than that in FIG the bath liquid.

The pH in the concentrate is reduced in a preferred method of reducing the

Concentration of interfering polyvalent cations in a bath liquid preferably with strong acids selected from sulfuric acid, hydrochloric acid, perchloric acid, nitric acid, sulfuric acid is particularly preferably used to adjust the pH. Analogously, in a process for reducing the concentration of interfering polyvalent anions in a bath liquid, the concentrate preferably has a pH greater than 11, more preferably greater than 12, but the pH value for avoiding

Degradation of the anion exchanger preferably not above 13.5. Furthermore, analogously, in a process for reducing troublesome polyvalent anions from a bath liquid, a ratio of the bath liquid to aqueous concentrate pHs of less than 1 is preferred, in particular the pH of the concentrate is at least one unit greater than the one in the bath.

The pH in the concentrate is reduced in a preferred method of reducing the

Concentration of interfering polyvalent anions in a bath liquid preferably with alkalis selected from sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, ammonia adjusted, more preferably sodium hydroxide is used to adjust the pH.

These measures with regard to the acidity or the alkalinity of the concentrate enable a high concentration of the interfering polyvalent ions in the concentrate.

The abovementioned preferred embodiments of methods according to the invention relating to the composition of the concentrate are applied in an analogous manner to US Pat

Composition of the electrolyte also preferred embodiments of the

inventive method with respect to the electrolyte.

An improved concentration of the interfering polyvalent ions in the concentrate can also be achieved by virtue of the fact that the membranes of the liquid streamed from the bath liquid are in contact with each other Membrane stack in the stacking direction are alternately selectively permeable to mono- and polyvalent ions.

An inventively preferred method for reducing the concentration of interfering polyvalent cations in the bath liquid is characterized in that the

Diaphragms of the series of membranes, within which each membrane is laminar flows on one side of the bath liquid and are on the cathode side facing the aqueous concentrate are in contact or in contact with the aqueous electrolyte, selectively permeable to polyvalent cations, preferably interfering polyvalent cations while the membranes of the series of membranes, within which each membrane is laminar flowed on one side of the bath liquid and which are flown on the anode-facing side of the aqueous concentrate or in contact with the aqueous electrolyte, are selectively permeable to monovalent cations.

The analogous preferred method for reducing the concentration of interfering polyvalent anions in the bath liquid is characterized in that the membranes of the series of membranes within which each membrane is laminar flowed on one side of the bath liquid laminar and on the cathode side facing the aqueous concentrate be flown or are in contact with the aqueous electrolyte, are selectively permeable to monovalent anions, while the membranes of the series of membranes, within which each membrane is laminar flowed on one side of the bath liquid and are flown on the anode side facing the aqueous concentrate or in contact with the aqueous electrolyte, being selectively permeable to polyvalent anions, preferably interfering polyvalent anions.

Selectively permeable ion exchange membranes are commercially available and are based on so-called chelating resins, which have a higher affinity for certain interfering polyvalent ions or certain monovalent ions in the concentrate and electrolyte. In this preferred variant of the process according to the invention, it is achieved that preferably polyvalent ions migrate into the concentrate or the electrolyte, conversely, however, the migration from the concentrate or electrolyte into the bath liquid is inhibited so that an overall concentrated concentration of the polyvalent ions in the concentrate takes place.

The method according to the invention is particularly advantageous when the interfering polyvalent ions of the bath liquid have a charge opposite to the surface charge of the dispersed constituents of the bath liquid. At the interface of the invention to be used ion exchanger for bath liquid then creates an electrical

"Donnan potential", which causes electrostatic repulsion of the dispersed components, causing blocking of the ion-exchanging membranes by migration or electrostatic growth of the dispersed constituents counteracted. Thus, this effect always comes into play when the surface charge of the dispersed constituents is negative in the case of the inventive use of cation-exchanging membranes and positive in the case of

inventive use of anion-exchanging membranes.

Preferred processes according to the invention therefore relate, on the one hand, to the removal of interfering polyvalent anions from bath liquids containing a cationically dispersed solids content and, on the other hand, to the removal of interfering polyvalent cations from bath liquids containing an anionically dispersed solids content, the

Solid content preferably comprises at least one dispersed organic binder and / or at least one dispersed inorganic solid.

In this context, therefore, in particular processes for the removal of interfering polyvalent anions, for example of phosphate ions, from dipping paints containing a cationically dispersed organic binder system, for example cathodic dipcoats (KTL), and methods for removing interfering polyvalent cations, such as zinc Aluminum and iron ions, from dip paints containing an anionically dispersed organic binder system, for example, from anodic coating (ATL), preferably.

It has also been found that the inventive method using a cell stack consisting exclusively of cation exchangers is ideal for the regeneration of autophoretic baths, the acidic aqueous

Represent compositions containing an anionically dispersed organic binder and iron (III) ions and preferably additionally free fluoride ions. Anionically dispersed organic binders have a negative zeta potential, ie a negative surface charge. Typical autophoretic baths are described, for example, in the publications US Pat. No. 7,138,444 B2 (claim 11, column 13, line 43 to column 14, line 28) and US Pat

WO 2010/066785 (page 5, line 10 to page 6, line 7, page 19, lines 1 to 29), to which reference is hereby explicitly made, in particular those disclosed therein

water soluble components of the autophoretic compositions and their relative proportions to each other are prototypical of the bath liquids to be worked up in the present invention.

In aqueous compositions suitable for autophoretic coating of

Metal surfaces of iron, zinc and aluminum are set with the binder system, is in the process engineering application, a strong accumulation with polyvalent cations of the metals iron, zinc and aluminum due to the Anbeizens to

coating metallic surfaces instead. This enrichment leads to a

Destabilization of the binder system dispersed in the autodepositing bath such that Limit values for the concentration of these polyvalent cations in the bath liquid must be adhered to and these polyvalent cations are interfering ions in the context of the present invention.

To reduce the proportion of polyvalent cations in such aqueous

autophoretic baths, in particular for reducing the proportion of iron ions,

Aluminum ions and zinc ions, a method according to the invention is particularly suitable

- In which a volume flow V _{B of} the bath liquid from the aqueous bath containing the bath liquid and a volume flow V _{K of} an aqueous concentrate, which preferably contains less than the critical concentration of iron ions, aluminum ions or zinc ions, from a concentrate reservoir vorratend the concentrate is fed into a cell pack for electrodialysis containing a membrane stack which comprises only cation exchangers and is bounded on both sides in the stacking direction by two electrically conductive current collectors,

- In which the volume flows V _B and V _K within the cell packet in partial volume flows δ, (ν _Β ) and δ, (ν _κ ) decay spatially separated from each other orthogonal to the surface normal of a series of membranes of the membrane stack by that of immediately adjacent and from each other spaced membranes of this series formed segments

pass through, wherein segments of the series of membranes through which only a partial volume flow δ, (ν _Β ) flows through the bath liquid, with such segments of the series of membranes through which only a partial volume flow δ, (ν _κ ) of the concentrate

flows through, alternating in the stacking direction, wherein the bath liquid within the segments of the series of membranes laminar flows adjacent membranes,

- In which each of the outer membranes of the membrane stack on the immediately

adjacent pantograph side either with an aqueous

Electrolyte is in contact, which is spatially separated from the aqueous concentrate and the bath liquid by the segment formed by the respective current collector and the respective outer membrane, or also with a partial volume flow δ, (ν _κ ) of the aqueous concentrate is flown,

- In which temporarily or permanently an electrical voltage is applied to the electrically conductive current collector, which are in contact with the aqueous electrolyte and / or the aqueous concentrate, wherein the electrical voltage is sufficiently large to the electrolytic decomposition of the aqueous electrolyte and / or of the concentrate

bring about,

- And in which the partial volume flows δ, (ν _Β ) of the bath liquid after passing through the

Membrane stack are pooled and fed back into the aqueous bath, while the Sub-volume flows δ _ί (ν _κ ) of the aqueous concentrate after passing through the membrane stack combined and transferred at least partially into the concentrate reservoir.

The abovementioned preferred embodiments for the method according to the invention for reducing the ionic strength or the concentration of specific polyvalent ions in an aqueous dispersion of organic binder and / or inorganic solid, if the reduction in the concentration of interfering polyvalent cations in the bath liquid is also directly involved for the aforesaid preferred method of reducing the proportion of polyvalent cations in autophoretic baths.

Surprisingly, it was found that even in autophoretic baths containing free fluoride ions, the proportion of iron and aluminum ions could be effectively reduced, although the said cations are present in the bath liquid to a significant extent as negatively charged fluorocomplexes. Obviously, in the

Process according to the invention also such disturbing polyvalent ions, which are in chemical equilibrium with oppositely charged complexes are removed to a satisfactory extent from the bath liquid.

In a further aspect, the present invention also relates to a cell packet for

Electrodialysis, which is suitable for the inventive method for reducing the ionic strength or the concentration of polyvalent ions in an aqueous dispersion of organic binder and / or inorganic solid.

Such a cell pack for electrodialysis comprises a membrane stack consisting of a number n of membranes and n + 1 area membrane separators, each having a frame which is a fluid-orthogonal to the stacking direction

Interior limited, with the n + 1 membrane spacers and the n membranes in

Stacking direction are arranged alternately, all membranes are cation exchangers or all membranes anion exchangers and at least part of

Membrane spacers, which are not outer spacers of the stack, are selected from laminar flow membrane spacers configured to have in the interior space with each of the respective immediately adjacent membranes a plurality of spaced-apart linear contact areas, at least one of the immediately adjacent ones Membranes formed linear

Contact areas are rectilinear to each other and do not cross and the average distance between the linear contact areas to each other not smaller than the spacing of the through these membrane spacers from each other separated membranes in the direction of their surface normal.

The interior of the membrane spacers is fluid-permeable according to the present invention, when a fluid can flow through the interior of the spacer in at least one direction orthogonal to the stacking direction of the membranes entirely.

A membrane spacers for laminar flow according to the invention allows a fluid having a dynamic viscosity of at least 0.8 mPas when flowing through the

Membrane spacer with an average flow rate of not more than 0, 1 m / s outside a laminar boundary layer substantially the course of the

Spacer follows spaced and immediately adjacent membranes and the

Flow does not tear off or swirled, so that a stationary flow is formed within the membrane spacer.

Those membrane spacers which are not outer spacers of the stack have according to the invention in the space bounded by the frame with the respective

immediately adjacent membranes then a plurality of rectified line-shaped contact areas, when each of the line-shaped contact areas with the respective

Mentally mind by rotation by not more than 45 °, preferably not more than 20 ° relative to each of the other contact areas can be aligned in parallel.

The cell package according to the invention for electrodialysis is characterized in that it

Laminar flow membrane spacers comprising, due to their linienformigen contact areas with at least one of the spaced membranes and due to the intended minimum spacing of these linienformigen contact areas to each other allow a directed flow of a fluid with a nearly homogeneous flow field, so that a fluid having a dynamic viscosity of at least 0.8 mPas neither fluidized nor laminar at a mean flow rate of not more than 0.1 m / s

Forming boundary layers that extend far into the fluid-permeable interior. The use of such a cell stack in a method according to the invention provides the advantage that the bath liquid flows through the membrane spacers for

Laminar flow is exposed to only a low shear stress and therefore dispersed in the bath liquid solids are not brought to coagulation.

In this context, a cell packet is preferred in which the membrane spacers for laminar flow on the immediately adjacent membranes in the stacking direction At least 10 ^"3 m apart to allow only low shear forces within the segment at medium flow rates of a fluid of not more than 0.1 m / s.

In a preferred embodiment of the cell stack, the membrane spacers for laminar flow in the cell stack are aligned identically along the stacking.

Accordingly, it is preferred that the membrane spacers are aligned identically for laminar flow in the cell packet with respect to their linienformigen in the respective interior, rectified to each other and not crossing contact areas. The laminar flow membrane spacers are in the preferred orientation when each of these linear contact areas in the interior of such a spacer is thought to rotate by not more than 45 °, preferably not more than 20 °, from each individual linear contact area of the interiors of the others

Membrane spacers for laminar flow can be aligned in parallel.

The same orientation of the membrane spacers for laminar flow allows that the partial volume flows δ, (ν _Β ) can be fed in each case in the same place in the cell packet in the corresponding segment and accordingly flow out of the segment at respectively same points of the cell packet.

Furthermore, the membrane spacers for laminar flow in the cell stack are preferably stacked so that their interior linear, rectified to each other and not crossing contact areas that they at least one of the immediate

Have adjacent membranes, along the stacking always on the same side with the immediately adjacent membranes in contact. By this preferred

Arrangement of the membrane spacers in the cell stack can be achieved in the process of the invention an optimal laminar flow of those membrane within the flowed through by the bath liquid segments in the surface near due to the electric field enrichment of the dispersed Festoffanteile done so that coagulation by the low shear stress in this area can be effectively suppressed. For example, anionically dispersed binder constituents accumulate on the anode-facing side of the membranes within the segments through which the bath liquid flows, so that already an optimized flow only at these interfaces, which with the help of the special design and orientation of the membrane spacers for

Laminarströmung is brought about, can prevent coagulation of binder components in a method according to the invention.

Of course, it is generally preferred if each membrane spacer for

Laminar flow in the interior with the respective two immediately adjacent Membranes having a plurality of spaced-apart line-shaped contact areas, wherein the respective linear contact areas with one of the immediately adjacent membranes rectified to each other and do not intersect and the mean distance of the respective linear contact areas with one of the immediately adjacent membranes to each other not smaller than the spacing of the is by the respective membrane spacers separate membranes in the direction of their surface normal.

Likewise, the membrane spacers for laminar flow in the interior should have as few contact areas with the immediately adjacent membranes, which promote a turbulence when flowing through a fluid along the linear contact areas. Consequently, a cell packet is preferred in which the membrane spacers for laminar flow in the interior each have no other contact areas of another type, for example punctiform contact areas with one or both of the respective immediately adjacent membranes whose mean spacing to each other is less than twice the spacing of the immediately adjacent membranes to each other, and preferably each have no other contact areas of another kind with the respective immediately adjacent membranes.

In particular, it is preferred that the linear contact areas of the

Membrane spacers for laminar flow in a cell package according to the invention are rectilinear and preferably at least a length of at least 50%, more preferably at least 80% of the extent of the interior in the direction of the rectilinear

Have contact area.

In a preferred embodiment of the cell stack, the membrane spacers for laminar flow along the stacking direction do not follow one another directly, since, when the cell stack is used in a method according to the invention, segments which are traversed by the bath liquid are always separated from one another by segments through which the concentrate flows. so there is no need to equip the cell stack so that all membranes are spaced by spacers for laminar flow. It is even advantageous to design those segments, which are flowed through by the concentrate, by appropriate membrane spacers so that a turbulence of the concentrate is achieved in order to ensure a rapid mass transfer with the strongest possible convection within the segment on the one hand and on the other hand, the expansion of concentration gradients minimize. Accordingly, a cell packet according to the invention is particularly preferred which comprises a membrane stack consisting of an even number n of membranes, wherein at least each second membrane spacer of the cell stack in the stacking direction, more preferably only each second membrane spacer of the cell stack in the stacking direction is a membrane spacer for laminar flow.

In a preferred cell package where only each is second in the stacking direction

Membrane spacer of the cell stack is a membrane spacers for laminar flow, is also the following condition for the spacing of the membranes through the

Spacer fulfilled before:

d ² - x (V _L )

Is greater than 3, preferably greater than 4, wherein

d ² - x (V _:)

I

d _L : the spacing of the membranes by membrane spacers for

Laminar flow in the direction of the surface normal of the membranes [m], ie: the spacing of the membranes by membrane spacers, the no

Spacers for laminar flow and no outer spacers are, in the direction of the surface normal of the membranes [m], and

x (Vi; V | _): the respective segment volume factor, which is the fraction of free

fluid-permeable volume within the segment volume spanned by the membrane spacer and the immediately adjacent membranes indicates [0 <x (Vi; V _L ) i 1]. The segment volume corresponds to the volume bounded by the frame of a membrane spacer and the immediately adjacent membranes. This is the respective one

Segment volume equal to the volume of the interior of the corresponding membrane spacer. The segment volume factors x (Vi; V _L ) are when using a Zellpaktes invention in one

according to the invention with the segment volume factors x (V _K , V _B ) identical.

If this additional condition is satisfied, then the segment volume will be

Membrane spacers, which are not laminar flow spacers and outer spacers, promote rapid convection as they flow through a fluid. The rapid convection is in the use of such a cell stack in a method according to the invention again advantageous for effective mixing of the concentrate in the segments that no membrane spacers for laminar flow and no outer spacers are, at the same time present laminar flow of the

Bath liquid in the remaining segments of the cell packet.

It is likewise preferred that the membrane spacers for laminar flow in the cell pack are arranged relative to one another in such a way that a rectified laminar flow flows along the linear contact regions of all the spacers with the respective ones directly

adjacent membranes takes place. In this way, a uniform direction of the partial volume flows can be realized by these membrane spacers.

A cell pack of the invention is particularly well suited for use in a process for reducing ionic strength in bath liquids containing a dispersed solids fraction when each stacked laminar flow laminar spacer is bounded on one side by a membrane which is selectively permeable to polyvalent ions , and bounded in the stacking direction, similarly to the other side, by a membrane which is selectively permeable to monovalent ions.

The membrane spacers for laminar flow are preferably configured in their limited by the frame interior space so that they have a plurality of spaced-apart spacer elements, wherein at least one fixing element is provided which connects a spacer with a respective immediately adjacent spacer element to a positional fixation of the spacer elements to each other and wherein each spacer member has a membrane contact region for linear contact of either an immediately adjacent or spaced diaphragm or two

opposite membrane contact areas for linear contact of both immediately adjacent or spaced membranes, all membrane contact areas of all spacer elements for linear contact only one of the immediately adjacent membranes orthogonal to the stacking direction and rectified to each other.

The spacers are preferably formed as a bar-shaped webs, which are connected by one or more fixing elements transversely to the linear orientation of the webs together.

The width of the linear membrane contact areas of the spacer elements of a

Membrane spacer for laminar flow is preferably not greater than 5-10 ^"3 m, more preferably not greater than 10 ^{" 3} m, but is preferably at least 2-10 ^"4 m.

Furthermore, it is preferred that the fixing elements are connected to the spacer elements such that the fixing elements of the membrane spacers in the interior no Have membrane contact areas for linear contact at least one of the immediately adjacent membrane, which cross a contact region of one or more of the spacer elements, and that the fixing elements particularly preferably have no membrane contact area for linear contact in the interior at least one of the immediately adjacent membrane, in particular, the fixing elements have none Membrane contact area in the interior to touch at least one of the immediately adjacent membrane.

Furthermore, according to the invention, such cell packages are preferred in which the spacer elements of the membrane spacers for laminar flow divide the segment volume or the interior of the spacers between two membranes immediately adjacent or spaced apart by the membrane spacers into a plurality of smaller, orthogonal, spatially separated individual volumes orthogonal to the stacking direction.

In accordance with the invention, cell bundles are preferred in which each membrane spacer for laminar flow has a segment volume factor x (V _L ) of at least 0.5, especially of at least 0.75.

Basically, those cell packets are preferred whose membrane surfaces available for mass transfer are maximally large. On the other hand, the membrane spacers for spacing immediately adjacent membranes must have contact areas therewith. In a further preferred embodiment of the cell stack, the membrane spacers are therefore configured such that the contact surfaces of the membrane contact areas of all

Distance elements in the interior of the spacer with one of the immediately adjacent membranes in the sum not more than 50% of the enclosed by the frame of the spacer respective membrane surface amount.

In accordance with the invention, cell bundles are preferred in which each membrane spacer which is not a laminar flow membrane spacer and external membrane spacer has a segment volume factor x (V |) of less than 0.5, more preferably less than 0.25. In a particularly preferred embodiment of the cell stack, all membrane spacers, which are not laminar flow membrane spacers and outer membrane spacers, have a plurality of intersecting line and / or point contact areas with one of the immediately adjacent membranes, the reciprocal area density of the intersections and punctiform ones

Contact areas on the respective immediately adjacent membranes smaller than 12 times, preferably smaller than 6 times the spacing of the immediately adjacent Diaphragm is square. As a result, the greatest possible thorough mixing of the fluid flowing through these spacers is achieved, resulting in high shear stresses compared to the flow field in the interior of the membrane spacers for laminar flow. Such membrane spacers, the no membrane spacers for

Laminar flow and no outer membrane spacers of the cell stack are preferably selected from a nonwoven, woven or knitted fabric, wherein the thread width is preferably less than 10 ^"3 m, more preferably less than 2-10 ^{" 4} m and the nonwoven, woven or knitted fabric also the spacing of immediately adjacent membranes is used and fleece, woven or knitted fabric thus have contact areas with two immediately adjacent membranes.

The frame of the membrane spacers serves to delimit the segment volume and thus performs a sealing function in the cell packet, by the escape of fluids flowing through the interior of the spacers, due to the limitation of the part of the immediately adjacent membranes, which may be in contact with the fluid.

Accordingly, the area formed frame may additionally have a thin elastic coating, which further improves the sealing of the cell stack.

The interior and the frame of the membrane spacers in the cell pack according to the invention can be rigidly connected to each other, so that the frame supports the spacer elements in the

fluid-permeable interior, which serve the spacing and contacting of the immediately adjacent membranes, already sufficiently or additionally stabilized. The frame can therefore in such an embodiment of the spacers the function of

Take over fixing, so that, if necessary, on fixing elements in the interior of the

Spacer can be dispensed with.

However, the interior and the frame of the membrane spacers in the cell pack according to the invention can also be designed in two parts, so that the frame and structural elements of the interior of the spacer represent individual components of the cell pack. Since the frame limits the fluid-permeable interior, the structural elements, such as spacing and fixing elements, which serve in the interior of the spacer for spacing and contacting the immediately adjacent membranes are inserted in a two-part design of the membrane spacers in the predetermined by the frame recess.

According to the invention, the frames of the membrane spacers are configured and arranged such that a partial volume flow of a fluid A, for example the bath liquid, can flow through the frame in the stacking direction through the respective interior of the spacer and a fluid B, for example the concentrate. For this purpose, the frame preferably each on opposite sides on the one hand passage openings, for example

Holes, and on the other hand distribution openings, such as T-holes or simple holes with a recess to the respective interior of the spacer, on. While a fluid can flow through the frame through the passage openings without reaching the interior of the spacer, the distribution openings serve for a partial volume flow of a fluid to flow through the interior of the spacer and on the distribution opening of the same spacer which is opposite and thus corresponding in the frame can flow out of the interior. For the application of the cell stack according to the invention in the method according to the invention is for the separation of

Bath liquid from the concentrate such a configuration of the cell pack preferred in which the frame of the membrane spacers are arranged alternately in the stacking direction in such a way that passage opening, for example, simple bore, on distribution opening,

for example, T-bore, and vice versa. The membranes of the cell stack then have in the contact area with the frame of the spacers at the points at which the frame has a passage opening or a distribution opening, also passage openings.

The membrane spacers in the cell pack according to the invention are preferably made of a material that does not corrode when used in a method according to the invention in the aqueous concentrate, aqueous electrolyte and the aqueous bath liquid, and therefore particularly preferably made of plastic or an inert metal.

In a preferred embodiment of the cell packet, the surface normals are

Membranes and the membrane spacers always in the stacking direction. Such

Embodiment is easy to implement in the construction of the cell stack and therefore preferred.

In a further embodiment, the membrane stack of the cell stack according to the invention is bounded on both sides in the stacking direction by two electrically conductive current collectors which rest on the two outer membrane spacers.

In addition, it is preferred that the membrane stack of the cell stack according to the invention is designed and enclosed in a housing such that the membrane stack can be traversed orthogonally to the stacking direction with the fluids A and B, the fluid A flowing exclusively through the membrane spacers for laminar flow

clamped and bounded by immediately adjacent membranes segment volumes flows without intermixing with the fluid B occurs within the housing, which flows exclusively through each other membrane spacers spanned and bounded by immediately adjacent membranes segment volumes. The electric current collectors are usually made of a metallic material and preferably have the same shape as the membranes and membrane spacers, more preferably the current collectors as well as the membranes and spacers are rectangular and plate-shaped. Than metallic materials graphite laminated metallic or metallically conductive support materials can be used, among other corrosion resistant alloys such as nickel-molybdenum alloys (Hastelloy ^®) or platinum or the like. In addition to the required corrosion resistance and abrasion resistance of the

Electrode material requires an economical method that the electrode materials for the corresponding electrochemical partial reaction for decomposition of the electrolyte should have the lowest possible overvoltage and therefore the current collector are often coated with precious metals of the elements platinum, ruthenium and / or iridium.

The invention is described below by way of example with individual exemplary embodiments with associated figures. It shows

1 shows a schematic structure of a preferred cell packet according to the invention in a fanned-out perspective view;

Figure 2 is a schematic perspective projection of a membrane spacer for laminar flow of a preferred cell stack according to the invention of Figure 1;

Figure 2a is a schematic cross-sectional view of the membrane spacer of Figure 2 along the plane A-A;

FIG. 3 shows a schematic perspective projection of a membrane spacer, which is not a spacer for laminar flow, of the preferred cell packet according to the invention according to FIG. 1;

Figure 4 is a schematic perspective projection of a membrane of the preferred cell stack of Figure 1;

Figure 5 is a schematic perspective projection of the cell packet according to Figure 1 limiting pantograph.

FIG. 1 shows a schematic structure of a preferred cell packet 100 according to the invention in a fanned-out perspective view. The cell stack 100 comprises a series of membranes 107 separated by membrane spacers 200, 300, the respective membrane spacers 200, 300 being connected directly to membranes 400a, 400b which are immediately adjacent, or to adjacent pantographs 500, 500 ^' segments 108a, 108b , 108c form. Each in the stacking direction second membrane spacers 200, 300 of the cell stack 100 is a membrane spacer for laminar flow 200. The cell stack 100 is bounded on both sides in the stacking direction by pantograph 500, which consist of stainless steel with the material number 1.4401 according to the European Standard (see Figure 5). All diaphragms 400a, 400b of the cell stack 100 have simple holes 109 in the edge region as passage openings which allow the concentrate and the bath liquid to flow through in the stacking direction. Accordingly, all diaphragm spacers 200, 300 along the stacking congruent with the simple holes 109 of the membranes 400a, 400b and along the opposite edge regions of the membrane spacers 200, 300 alternately distribution elements 1 10, which additionally allow the flow through the individual segments 108a, 108b, 108c, and simple holes 109 as passage openings, wherein in the stacking direction, the distribution elements 1 10 of a membrane spacer 300, 200 to a simple bore 109 of the immediately adjacent membrane spacers 200, 300 and vice versa. Simple bores 109 for the inlet 101, 102 and the outlet 103, 104 of the two volume flows V _{K of} the concentrate and V _{B of} the bath liquid are likewise located in the two current collectors 500. In such a cell pack 100 according to the invention, therefore, the volume flows V _K and V _B can be fed to the respective inlets 101, 102 on the current collector, which are then fed to the respective segments 108 of FIG

Cell packets 100 into the respective sub-volume flows δ, (ν _κ ) 105 and δ, (ν _Β ) 106 disintegrate, which in turn within the membrane spacers 200, 300 orthogonal to the stacking direction between adjacent with the distribution elements 1 10 adjacent edge regions

Membrane spacers 200, 300 run along the membranes 400 and then combined at the outlets 103, 104 can be removed as a volume flow V _K and V _B without intermixing of the two volume flows V _K and V _B takes place in the cell stack 100. All partial volume flows δ, (ν _κ ) 105 flow through the membrane spacers 300 of the segments 108b, 108c in this preferred embodiment, while all partial volume flows δ, (ν _Β ) 106 exclusively flow through the membrane spacers for laminar flow 200 of the segments 108a of the cell stack 100.

FIG. 2 shows a schematic perspective projection of a membrane spacer for laminar flow 200 of a preferred cell packet 100 according to FIG. 1. The membrane spacer for laminar flow 200 has a frame 203 and more in the Inner space 204 extending spacer elements, which are formed as webs 201 each having a straight membrane contact region 202. The frame 203 serves in this embodiment of the membrane spacer 200 both to limit the fluid-permeable interior 204 and as a fixing element, which connects the webs 201 formed as spacers with each other. On opposite sides of the frame 203 of the

Membrane spacer for laminar flow 200 are each alternately simple

Holes 205 as passage openings and T-holes 206 are inserted as distribution elements, wherein the T-holes 206 are inserted so that a partial volume flow of fluid through these T-holes 206 in the frame 203 bounded by the inner space 204 of the

Membrane spacer 200 and flow along the webs 201 through the inner space 204 to flow on the respective opposite side of the frame 203 by corresponding T-holes 206 from the inner space 204.

Figure 2a shows a schematic cross-sectional view of the membrane spacer 200 of Figure 2 along the plane A-A with the simple holes located in the frame 205 and T-holes 206, which in the frame 203 of the membrane spacer 200, the

fluid-permeable interior 204 limited, are embedded.

FIG. 3 shows a schematic perspective projection of a membrane spacer 300 of the preferred cell pack according to the invention according to FIG. 1, which is not a spacer for laminar flow. The membrane spacer 300 has a frame 303 and in the

Inner space 304 extending spacers, which are formed as fabric 301 with plain weave, so that point-shaped membrane contact areas 302 result. The frame 303 is realized as a material composite of the fabric 301 and a rubber-elastic material, so that the free spaces in the edge region of the fabric 301 are filled by the rubber-elastic material and the thickness of the frame 303 corresponds approximately to the tissue thickness. On opposite sides of the frame 303 of the membrane spacer 300 are alternately simple bores 305 as passage openings and simple bores with recess 306 inserted as distributing elements, wherein the recesses of the simple bores 306 of the distribution elements are embedded so that a partial volume flow of fluid through these holes 306 in the interior 303 bounded by the frame 303 of the membrane spacer 300 flow into and can flow through the interior 304 to on the respective opposite side of the frame 303 through

corresponding simple holes with recess 306 to flow out of the interior 304. FIG. 4 shows a schematic perspective projection of a membrane 400a of the preferred cell package 100 according to FIG. The membrane 400a has passage openings on opposite sides in the marginal area, on each side

Passage openings 406 to the segments 1 10 with membrane spacers for

Laminar flow 200 with passage openings 405 to the segments 1 10 with

Membrane spacers 300 that are not spacers for laminar flow,

alternate. The passage openings 405 and 406 are configured as simple bores. A corresponding schematic perspective projection of a membrane 400 b is identical to FIG. 4.

FIG. 5 shows a schematic perspective projection of one of the pantographs 500 delimiting the cell stack 100 according to FIG. 1, which has simple holes 505, 506 for the inlet or outlet of the volume flows V _K 105 of the concentrate and V _B 106 of the bath liquid in the edge area. In the simple holes 505, 506 electrically insulating sleeves 503 are embedded. The pantographs 500 are made of stainless steel with the

Material number 1.4401 according to European standard. Both the cell pack 100 limiting pantograph 500 are identical and differ in the operation of the method only by the fact that the simple holes 505, 506 of a pantograph 500, the inlet points of the flow rates V _K 105 of the concentrate and V _B 106 of the

Bath liquid in the cell pack 100 represent, while the simple holes 505, 506 of the opposite second pantograph 500 are the corresponding outlet points for the flow rates V _K 105 of the concentrate and V _B 106 of the bath liquid.

LIST OF REFERENCE NUMBERS

506 Simple bore for bath fluid

Claims

claims:

1. cell pack (100) for electrodialysis comprising a membrane stack consisting of a number n of membranes (400a, 400b) and n + 1 area formed

Membrane spacers (200, 300), each having a frame (203, 303) defining an interior (204, 304) fluid-permeable orthogonal to the stacking direction, the n + 1 membrane spacers (200, 300) and the n membranes (400a, 400b) are alternately arranged in the stacking direction, wherein all the membranes (400a, 400b) are cation exchangers or all membranes (400a, 400b) are anion exchangers and at least a part of the membrane spacers (200, 300) which are not outer spacers of the stack is selected from Laminar flow membrane spacers (200) configured to have in their fluid-permeable interior (204) a plurality of spaced apart linear contact regions (202) with each of the respective immediately adjacent membranes, the ones formed with at least one of the immediately adjacent membranes linear contact areas (202) rectified verla to each other and do not intersect and the mean distance between these line-shaped contact areas is not smaller than the spacing of the membranes separated by these membrane spacers (200) in the direction of their surface normals.

2. Cell pack (100) according to claim 1 comprising a membrane stack consisting of an even number n of membranes (400a, 400b), wherein at least each of the

Membrane spacers (200, 300) of the cell stack (100) which is a second membrane spacer in the stacking direction, preferably only each of the membrane spacers (200, 300) of the cell stack (100) being a stacked second membrane spacer, a laminar flow membrane spacer (200 ).

3. cell packet (100) according to one or both of the preceding claims, characterized

characterized in that the membrane spacers for laminar flow (200) in

Inner space (204) each have no further contact areas of another type with one or both of the respective immediately adjacent membranes whose middle

Spacing to each other is less than twice the spacing of the immediately adjacent membranes to each other, and preferably each have no further contact areas of another type with the respective immediately adjacent membranes. Cell pack (100) according to one or more of the preceding claims, characterized in that the contact areas (202) of the membrane spacers for laminar flow (200) in the interior (204) are rectilinear and preferably at least 50%, more preferably at least 80% the extension of the inner space (204) in the direction of the rectilinear contact region (202).

Cell pack (100) according to one or more of the preceding claims, characterized in that the membrane spacers for laminar flow (200) the immediately adjacent membranes in the stacking direction to at least 10 ^"3 m

spacing.

Cell pack (100) according to one or more of the preceding claims, characterized in that the membrane spacers for laminar flow (200) in

Interior (204) a plurality of spaced apart

Have spacer elements (201), wherein at least one fixing element (203) is provided, which connects a spacer element (201) with a respective immediately adjacent spacer element (201) to a positional fixation of

To ensure spacer elements (201) to each other and wherein each spacer element (201) has a membrane contact area for linear contact either an immediately adjacent membrane or two opposite

Membrane contact areas (202) for linear contact of both immediately adjacent membranes, all membrane contact areas (202) of all spacer elements (201) for linear contact only one of the immediately adjacent membranes orthogonal to the stacking direction and rectified to each other.

Cell pack (100) according to claim 6, characterized in that the at least one fixing element (203) is connected to the spacer elements (201) such that the at least one fixing element (203) of the spacer (200) in the interior (204) no membrane contact areas for at least one of the immediately adjacent membrane, which intersect a contact region (202) of one or more of the spacer elements (201), and that the at least one fixing element (203) of the membrane spacer (200) preferably in the interior (204) no

Have membrane contact area for linear contact at least one of the immediately adjacent membrane.

8. cell packet (100) according to one or more of the preceding claims, characterized in that each membrane spacer to the laminar flow (200) in the stacking direction is limited to one side of a similar to one side of a membrane selectively permeable to polyvalent ions, and in the stacking direction similar to the other Side is bounded by a membrane which is selectively permeable to monovalent ions.

9. cell packet (100) according to one or more of the preceding claims, characterized

characterized in that each membrane spacer (300) which does not

Membrane spacer for laminar flow is formed in the interior (304) as a nonwoven fabric (301) or knitted fabric.

10. A method for reducing the concentration of interfering polyvalent ions in one

aqueous bath containing a dispersed organic binder and polyvalent ions,

- In which a volume flow V _B (102) of the bath liquid from the aqueous bath containing the bath liquid and a volume flow V _K (101) of an aqueous

Concentrate from a concentrate reservoir vorratend the concentrate into a cell pack (100) for electrodialysis comprising a membrane stack of a plurality of spaced apart membranes (400a, 400b), which in the event that disturbing polyvalent cations are contained in the bath liquid, exclusively cation exchanger, and for the case in which disturbing polyvalent anions are contained in the bath liquid, comprising exclusively anion exchangers, and electrically conductive current collectors (500), which limit the stack of membranes on both sides in the stacking direction, are fed in,

in which the volume flows V _B (102) and V _K (101) within the cell stack (100) decay into partial volume flows δ, (ν _Β ) (106) and δ, (ν _κ ) (105) which are orthogonal to

Surface normals of a series (107) of membranes (400a, 400b) of the membrane stack through the segments (108a, 108b) formed by immediately adjacent and spaced apart membranes of the series (107) of membranes (400a, 400b) flow apart, wherein Segments (108a) of the series (107) of membranes (400a, 400b), through which only a partial volume flow 8i (V _B ) (106) of the bath liquid flows, with such segments (108b) of the series (107) of membranes (400a, 400b), through which only a partial volume flow δ, (ν _κ ) (105) of the concentrate flows, alternate in the stacking direction, wherein the bath liquid within the segments (108a) of the series (107) of membranes (400a, 400b) flows laminarly adjacent membranes . - Wherein each of the outer membranes of the membrane stack (400a) on the immediately adjacent pantograph (500) side facing either with an aqueous electrolyte in contact, by that of the respective

Current collector (500) and the respective outer membrane formed segment (108c) is spatially separated from the aqueous concentrate and the bath liquid, or also with a partial volume flow δ _ί (ν _κ ) (105) of the aqueous concentrate is flown,

- In the temporary or permanent electrical voltage to the electrical

conductive pantograph (500) is in contact with the aqueous electrolyte and / or the aqueous concentrate, wherein the electrical

Stress is sufficiently high to cause the electrolytic decomposition of the aqueous electrolyte and / or the concentrate,

- And in which the partial volume flows δ, (ν _Β ) (106) of the bath liquid after passing through the membrane stack combined and fed back into the aqueous bath, while the partial volume flows δ, (ν _κ ) (105) of the aqueous concentrate after

Passing through the membrane stack united and at least partially in the

Concentrate reservoir are transferred.

1 1. A method according to claim 10, characterized in that the ratio of mean flow velocity of the bath liquid in meters per second within the of the bath liquid with the partial volume flows δ, (ν _Β ) (106) flowed through segments (108a) of the cell stack (100) for spacing the membranes in the direction of their

Surface normals within these segments (106) in meters smaller than 100,

is preferably less than 20, wherein the average flow rate of the bath liquid is preferably not greater than 0, 1 m / s.

12. The method according to one or both of claims 10 and 1 1, characterized in that the following condition is fulfilled within the of the series (107) of the membranes (400a, 400b) formed segments (108a, 108b) of the cell packet: is greater than 3, preferably greater than 4, wherein

δ, (ν _Β ): the partial volume flow of the bath liquid (106) within the segment (108)

[m ³ / s],

δ, (ν _Β ): the partial volume flow of the concentrate (105) within the segment (108)

[m ³ / s], d _B , d _K : the spacing of the membranes of the respective segment (108 a, 108 b) in

Direction of their surface normals [m] and

x (V _K; V _B ): the segment volume factor that determines the proportion of free volume within

indicates the respective flowed through segment (108a, 108b)

[0 <x (V _K ; V _B ) <1].

13. The method according to one or more of claims 10 to 12, characterized in that the electrical voltage is applied pulse potentiostatically, wherein the pulse duration preferably in the range of 0.5 to 50 seconds, preferably in the range of 0.8 to 2 seconds, and the pulse resting phase is preferably in the range of 0.2 to 10 seconds, more preferably in the range of 0.4 to 1 second.

14. The method according to one or more of claims 10 to 13, characterized in that from an electrolyte reservoir vorratend the aqueous electrolyte

Volumetric flow V _{E of} the aqueous electrolyte is fed into the cell stack (100), which decays within the cell stack in partial volume flows δ, (ν _Ε ), orthogonal to

Surface normals of the outer membranes of the membrane stack by the current collector (500) and the immediately adjacent outer membranes formed segments (108c) of the cell pack (100) and after passing through the segments (108c) within the cell pack (100) combined and at least partially in the electrolyte reservoir are transferred.

15. The method according to one or more of claims 10 to 13, characterized in that only the volume flows V _B and V _K are fed into the cell stack (100), wherein by the current collectors (500) and the immediately adjacent outer membranes formed segments (108c) of the cell stack (100) in each case a partial volume flow δ, (ν _κ ) (105) flows through the aqueous concentrate, with the remaining partial volume flows δ, (ν _κ ) (105) of the aqueous concentrates passing through the segments ( 108b) of the series (107) of membranes (400a, 400b), after passing through the segments (108c) within the cell stack (100) is combined.

16. The method according to claim 15, characterized in that a cell packet (100) according to claim 2 is used and the partial volume flows δ, (ν _Β ) (106) of the bath liquid exclusively through those segments (108b) of the series (107) of membranes ( 400a, 400b) whose immediately adjacent membranes (400a, 400b) are spaced apart by membrane spacers to the laminar flow (200).

17. The method according to one or both of claims 15 and 16, characterized in that the concentration of a disturbing polyvalent ion type in the concentrate is below a critical concentration or held by continuously or discontinuously replacing partial volumes of the aqueous concentrate by an aqueous solution with a electrical conductivity of at least 1 mScm ^"1 containing no polyvalent ions, wherein for the critical concentration of a disturbing polyvalent ion type the following relationship applies:

ο ^ (Κ): critical concentration of the interfering polyvalent ion species

in the concentrate [mol / l]

c _s (B): concentration of the interfering polyvalent ion type

in the bath liquid [mol / l]

Zj Ui Ci (K): Products of charge number, ion mobility and concentration

a similar to the disturbing type of ion like charged ion type i im

concentrate

zj uj cj (B): products of charge number, ion mobility and concentration

a similar to the disturbing type of ion like charged ion type j

in the bath liquid

zi ' ^Z J charge number of the ion types i, j ui' ^U J ion mobility of the ion types i, j [m ² s ^"1 V ^{" 1} ]

' ^C J concentration of ion types i, j [mol / l]

18. The method according to one or more of claims 10 to 17, characterized in that the bath liquid contains an anionically dispersed binder and interfering polyvalent cations, wherein the interfering polyvalent cations are selected from zinc ions, iron ions or aluminum ions.

19. The method according to claim 18, characterized in that in the bath liquid

additionally free fluoride ions are contained.

Method according to one or both of Claims 18 and 19, characterized in that the membranes (400a, 400b) of the series (107) of membranes (400a, 400b) which are on the cathode side facing the aqueous concentrate or are in contact with the aqueous electrolyte, are selectively permeable to interfering polyvalent cations, while the membranes (400a, 400b) of the series (107) of membranes (400a, 400b), the the anode-facing side of the aqueous concentrate are flown or in contact with the aqueous electrolyte, are selectively permeable to monovalent cations.